1. Field of the Invention
The present invention relates to a light emitting diode (LED) and a manufacturing method thereof, and more particularly to a light emitting diode which includes an LED element and a fluorescent material which covers the LED element and a manufacturing method thereof.
2. Description of the Related Art
Among light emitting diodes there are light emitting diodes which emit white light (hereinafter, referred to as white light emitting diodes). Among the white light emitting diodes there are a white light emitting diode which is configured with an LED (Light Emitting Diode) element which emits blue light and a fluorescent material which emits yellow light (for example, a YAG-based fluorescent material, YAG: Yttrium, Aluminium, Garnet), and a white light emitting diode which is configured with an LED element which emits a near-ultraviolet ray and fluorescent materials of three colors of red, blue and green.
As for the white light emitting diode configured with the blue light emitting LED element and the fluorescent material which emits yellow light, a white light can be obtained when the blue light from the LED element and the yellow light from the fluorescent material are mixed up.
A plurality of white light emitting diodes like the one describe above are mounted for use on a printed circuit board. When a white light emitting diode is mounted on a printed circuit board, initially, an LED element is electrically connected to pads on the printed circuit board, and following this, a fluorescent material is formed in such a manner as to cover the LED element so mounted (for example, refer to JP-A-2000-223749).
The fluorescent material can be formed by a printing method using a metallic mask. In the case of the printing method, a metallic mask having an opening through which the LED element is exposed is disposed on the printed circuit board, and thereafter, a fluorescent material is formed in such a manner as to fill the opening.
However, since LED elements have individual differences, and different characteristics respectively (tone and luminous intensity, etc.), even when a fluorescent material of a substantially uniform thickness can be formed over a plurality of LED elements, the tone and luminous intensity become inconsistent among the white light emitting diodes. Thus, there is a problem that yield of white light emitting diodes is reduced.
In addition, when there exists unevenness in shapes (for example, height, width and the like) of LED elements, or when the position accuracy of an LED element relative to pads formed on a printed circuit board is not good, it becomes difficult to form fluorescent materials of a substantially uniform thickness over the LED elements, resulting in a problem that the yield of white light emitting diodes is deteriorated due to variation in thickness.
Furthermore, in the case of a white light emitting diode having a high luminance, a large current is applied to the LED element, resulting in a problem that the LED element is heated to such an extent that the white light emitting diode fails eventually.